Theory
Page 97 of 110
Section 4: Theory
4.1 Introduction
The model 1910 Inductance Analyzer uses a principle of measurement which is based upon a
technique developed by IET Labs. for its 7000 Series of Precision LCR Meters. In particular, the
model 1910 employs digital techniques for signal generation and detection, as well as for the
more usual data processing, user input output and remote communications functions. The
following section provides a general overview of the model 1910 measurement technique for one
familiar with impedance measurement and modern instrumentation. Subsequent sections provide
detailed descriptions of operation, circuit block diagrams and system level control signals.
4.1.1 Description of 1910 Inductance Analyzer
In the model 1910 Inductance Analyzer, the voltage across the device under test (DUT) is
measured, and the current through the DUT is measured across a reference resistor Rs which
carries substantially the same current. The voltage across the DUT is Ex and the voltage across
Rs is Es. Both voltages are sampled many times per cycle of the applied sine wave excitation. Ex
and Es are essentially simultaneously sampled. There are five reference resistors in the 1910; the
one used for a particular measurement is the optimal resistor for the device under test, frequency
and amplitude of excitation. These characteristics are stored in the 1910 in non-volatile memory.
For both Ex and Es a real and imaginary (in phase and quadrature) component are computed
mathematically from the individual sample measurements. The real and imaginary components
of Ex and Es are with respect to a reference of arbitrary phase, so that by themselves they are
meaningless. Any differences in the voltage and current detection and measurement process, as
well as non-idealities in the sampling and digitization process, are corrected via software using
calibration data. The real and imaginary components of Ex (Ex
r
and Ex
i
) are combined with the
real and imaginary components of Es (Es
r
and Es
i
) and the known characteristics of the reference
resistor to determine the apparent complex impedance of the DUT using complex arithmetic.
Further calculations are made to remove the characteristics of the test fixture (“stray”
capacitance and conductance and series resistance and inductance) if simple SHORT and OPEN
calibration measurements have been made by the operator. These corrections are stored in non-
volatile memory in the 1910 and are retained during power down and power up.
The detection and excitation circuitry is configured for each measurement by an embedded
computer. For the excitation circuitry this includes frequency of excitation, DC bias current, and
excitation level. Frequency is varied from 20Hz to 1MHz. Excitation level is between 20mV and
1V (open circuit).
Summary of Contents for 1910
Page 8: ...Page 4 of 110...
Page 10: ...Page 6 of 110...
Page 34: ......
Page 100: ......
Page 107: ...Theory Page 103 of 110 Figure 4 4 Detector Circuits Es IL Ex PL PH Voltage Current...
Page 108: ...Page 104 of 110 Theory Figure 4 5 Digital Signal Processor Es Ex CPU DSP A D Vin A Vin B...